Card 16: Sorting

Module 6: Advanced Techniques

1 The Hook

How does Netflix rank Top 10 movies? How does Amazon sort price Low-to-High?

They use Sorting Algorithms.

Goal: Put numbers in order (e.g. 1, 2, 3).
Method: Compare and Swap.

2 Worked Example: The Swap

To sort, we often need to swap two items.

# We want to swap A and B

a = 5

b = 10

# Use a Temp variable

temp = a # Save 5

a = b # a becomes 10

b = temp # b becomes 5

PREDICT

What happens to the list?

nums = [8, 2, 5]
if nums[0] > nums[1]:
nums[0] = nums[1]
nums[1] = 8
print(nums)

Interactive Editor

main.py

# Bubble Sort Pass
nums = [5, 1, 4, 2, 8]
print(nums)

# Compare first two
if nums[0] > nums[1]:
    # Swap them
    t = nums[0]
    nums[0] = nums[1]
    nums[1] = t

print(nums)

Terminal Output

> _

BRONZE (MODIFY)

🥉 Swap Shop

1. nums = [10, 5, 20].
2. The code tries to swap index 0 (10) and index 1 (5).
3. Fill in the missing variables to complete the swap.

bronze.py

nums = [10, 5, 20]
t = nums[0]
nums[0] = ...
nums[1] = ...
print(nums)

> _

SILVER (FIX)

🥈 Broken Logic

This code only swaps if nums[0] < nums[1] (Less Than).
1. We want to sort Low-to-High.
2. So we should swap if index 0 is GREATER than index 1.
3. Fix the symbol from < to >.

silver.py

nums = [9, 2, 5]
if nums[0] < nums[1]:
    t = nums[0]
    nums[0] = nums[1]
    nums[1] = t
print(nums)

> _

GOLD (MAKE)

🥇 Max Finder

1. Create a list vals = [10, 50, 20, 5].
2. Set highest = 0.
3. Loop through the list: for x in vals:.
4. Inside loop: if x > highest: then highest = x.
5. Print highest.

gold.py

vals = [10, 50, 20, 5]
highest = 0

for x in vals:
    # Check if x is greater than highest
    ...

print(highest)

> _

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